I was charging my A/C system with 134a today, through the low side valve. Gauge was reading 35 psi with the compressor on, and the system took the first 12 oz. can without too much problem. Went to add the second can also through the low side, and the system only took about 2oz., and wouldn't take any more. I'm reading 45 lbs low side and 200 lbs. high side, and probably only have about 14oz.'s of 134a in the system. A/C temp waivers from 48F to about 58F from the center vent.

My pressure readings appear to be in the range, but 14 oz's seems way too low to be correct. Is there a way to have the system take more 134a?

 

Adam,

If you were starting with a recently opened system, or one which was empty, did you pull a vacuum (vacuum the system down) before charging?

Greg

 

Adam,

You MUST start with a hard vacuum. If you do, you can put most of a can (12 oz.) into the system without the compressor running.

If the system operates correctly, the compressor will pull the low side very low when the system is undercharged.

If the low side is too high, and the high side is too low, the usual problem is either a faulty compressor (perhaps broken reed valves, slipping clutch, damaged piston) or a faulty expansion valve (valve staying open too much).

You didn't say whether you have the rear A/C.

Up to a build date of July '88, the standard A/C should be charged with about 30 ounces of R-134a, with rear A/C, about 34 or 35 ounces.

After a build date of July '88, standard should be about 27 ounces of R-134a, rear A/C about 33 or 34 ounces.

I believe the difference is due to a change in the compressor used, so that should be taken into account if you have changed the compressor.

As of MY '93, standard should have 860 g. R-134a, rear A/C 1050 g.

 

My 928 has the rear A/C.

The compressor, lines, dryer and related O-rings are all new. Vaccuumed out the system, then held the vaccuum over night to check for leaks. It held.

The very first thing I did was put in two additional ounces of esther oil. I then bypassed the low pressure switch, turned the front and rear A/C on max, fired up the compressor and started adding in the R134a.

In the posts and tips that I have read, I didn't gather that a vaccuum was required to get the first can in. I thought I came across a few posts where people had stated that they were able to charge their systems from just running the compressor.

At any rate, I'm in this to learn how to do it right. So should a vaccuum out the system again, and start over by charging the first can under a hard vaccuum?

I must say, even though the system isn't 100%, it sure is nice to have functioning A/C in a triple black 928

 

Adam,

You had a vacuum in the system - did you then let in air, so that you had no vacuum when you started charging? If so, yep - start over.

There must be no air or moisture in the system.

 

When I started up the car, the vaccuum turned to pressure. The low side gauge went from about 20" vaccuum (some of the vaccuum was used to load the ester oil) to 35 psi.